1. Field of the Invention
The present invention relates to a vehicle generator controller for gradually increasing the current generated by a generator by gradually increasing a field current by intermittently operating a switching element when a battery voltage is dropped by the impose of an electric load, and more specifically, to a vehicle generator controller by which the drop of the battery voltage is sufficiently suppressed when the electric load is turned on.
2. Description of the Related Art
Conventionally, in a vehicle generator controller, since a torque shock is caused when a generated current is increased in instant response to the drop of a battery voltage, the current generated by a generator is gradually increased by gradually increasing a field current by the gradual increase of a conducting ratio (duty) executed by the intermittent operation of a switching element.
FIG. 4 is a circuit diagram showing a conventional vehicle generator controller disclosed in U.S. Pat. No. 5,886,500.
In the drawing, a generator 1 driven by an internal combustion engine (not shown) includes an armature coil 101 and a field coil 102 and is mounted on a vehicle.
The rectifier 2 of the generator 1 for subjecting the ac output from the generator 1 to full wave rectification includes an output terminal 201 acting as a main output terminal, an output terminal 202 for exciting the field coil 102 and an output terminal 203 for the ground.
A controller for controlling the field current IF (generated current) of the generator 1 is composed of a voltage regulator 4 for regulating the output voltage (battery voltage VB) from the generator 1 to a predetermined value, a smoothing circuit 5 for smoothing the voltage detecting signal D of the battery voltage, a comparison circuit 7 operating in response to the output signal level from the smoothing circuit 5 and a constant voltage power supply circuit 8 for creating a constant power source A.
The smoothing circuit 5 and the comparison circuit 7 constitute a gradual increase control circuit for gradually increasing the field current IF of the generator 1 when the battery voltage VB drops.
A battery 9 mounted on the vehicle is charged by the output created by the generator 1 and rectified through the rectifier 2. A key switch 10 is connected to an end of the battery 9. The electric load 11 of the vehicle such as head lights, an air conditioner and the like is connected between both the ends of the battery 9. A switch 12 for imposing the electric load 11 is inserted between an end of the electric load 11 and one of the ends the battery 9.
The voltage regulator 4 includes resistors 401, 402 for creating a detected voltage Vb by dividing the voltage VB of the battery 9, resistors 403, 404 for creating a reference voltage VR by dividing the constant power source A, a comparator 405 for outputting a voltage detection signal D by comparing the detected voltage Vb with the reference voltage VR, an emitter-grounded transistor 407 inserted to the field coil 102 in series therewith for intermittently controlling the field current IF, a diode 408 for absorbing the surge caused by the intermittent operation of the transistor 407 and a resistor 409 inserted between the base of the transistor 407 and the collector thereof.
The voltage regulator 4 includes an emitter-grounded transistor 410 having a collector connected to the base of the transistor 407, a pair of diodes 411, 412 inserted in series between the output terminal of the comparator 405 and the base of the transistor 410 in inverted polarity and a resistor 413 inserted between the constant power source A and the point where diode 411 is connected to the diode 412.
The smoothing circuit 5 includes a pair of diodes 511, 512 connected in series to the output terminal of the comparator 405 in inverted polarity, a charging resistor 513 inserted between the constant power source A and the point where the diode 511 is connected to the diode 512, a capacitor 503 inserted between the cathode of the diode 512 and the ground and a discharging resistor 515 connected in parallel with the capacitor 503.
The comparison circuit 7 includes a triangle generator 701 for creating a triangle voltage VT, a comparator 702 for outputting a gradual increase control signal E by comparing the voltage VC of the capacitor 503 with the triangle voltage VT, an emitter-grounded transistor 712 inserted between the base of the transistor 407 and the ground and a resistor 713 inserted between the point where the base of the transistor 712 is connected to the output terminal of the comparator 702 and the constant power source A.
With this arrangement, the comparison circuit 7 gradually increases the field current IF by intermittently operating the transistor 407 to thereby gradually increase the current generated by the generator 1.
The gradual increase control signal E which is output from the comparator 702 gradually increases the conducting duty of the transistor 407 in response to the voltage which is output from the smoothing circuit 5, that is, to the capacitor 503 voltage VC to thereby gradually increase the field current IF.
A series circuit composed of a diode 111 and an initially exciting resistor 112 is inserted between the key switch 10 and an end of the field coil 102.
The constant voltage power supply circuit 8 is composed of a series circuit inserted between the key switch 10 and the ground and including a pull-up resistor 801 and a Zener diode 802.
With this arrangement, when the key switch 10 is turned on, the constant power source A is created from the point where the pull-up resistor 801 is connected to the Zener diode 802 based on the battery voltage VB.
Next, operation of the conventional vehicle generator controller shown in FIG. 4 will be described with reference to the waveform view of FIG. 5.
First, when the key switch 10 is turned on, the battery voltage VB of the battery 9 is turned on the Zener diode 802 through the resistor 801 and the constant power source A which is clamped by the Zener diode 802 is created from the point where the resistor 801 is connected to the Zener diode 802.
With this operation, although the controller of the generator 1 is made to an operable state, since the generator 1 does not yet start power generation, the signal level on the non-inverting input terminal (+) side of the comparator 405 in the voltage regulator 4 is lower than the reference voltage VR on the inverting terminal (-) thereof and accordingly the comparator 405 outputs the voltage detection signal D of a level.
At the time, since the capacitor 503 in the smoothing circuit 5 is not charged, the voltage VC has a zero potential. Therefore, the signal level on the non-inverting input terminal (+) side of the comparator 702 in the comparison circuit 7 is lower than a triangle voltage VT and the gradual increase control signal E is fixed to a low level and the transistor 712 remains in an off-state.
Consequently, the transistor 407 is turned on and the field current IF flows to the field coil 102 to thereby put the generator 1 to a power generation possible state.
When the internal combustion engine starts operation and the generator 1 starts power generation by being driven by the internal combustion engine, the signal level on the non-inverting input terminal (+) side of the comparator 405 in the voltage regulator 4 is increased by the increase of the battery voltage VB. When the signal level on the non-inverting input terminal (+) side becomes higher than the reference voltage VR, the voltage detection signal D is switched from the low level to a high level and the transistor 407 is switched from a conducting state to a shut-off state.
As described above, the voltage regulator 4 detects the battery voltage VB at all times and when, for example, it detects the drop of the battery voltage VB, it increases the conducting ratio of the transistor 407 through the comparator 702.
Since the field current IF is increased by the increase of the conducting ratio of the transistor 407 and the battery 9 is charged by the increase of the output from the generator 1, the battery voltage VB is controlled to a constant rated voltage.
When, for example, the switch 12 is turned on and the electric load 11 is turned on, the comparator 702 is operated and the field current IF is increased by the drop of the battery voltage VB.
At the time, although the comparator 405 which responds to the battery voltage VB creates the voltage detection signal D of a low level by increasing the conducting duty of the field current IF, since the discharging time constant of the smoothing circuit 5 is set longer than the charging time constant thereof, the comparator 702 in the comparison circuit 7 increases the conducting ratio of the transistor 407 so as to gradually increase the duty as shown in FIG. 5.
Therefore, the field current IF gradually increase as the conducting ratio of the transistor 407 increases so that the output from the generator 1 gradually increases while suppressing a response shock.
However, when the gradual increase control is simply executed just after the electric load 11 is turned on, the voltage drop caused by the supply of the power to the electric load 11 cannot be instantly compensated.
As are result, the battery voltage VB greatly drops just after the electric load 11 is turned on as shown in FIG. 5 and the quantity of light of, for example, head lights is lowered, which makes the driver uncomfortable.
To suppress the drop of the battery voltage VB, there is proposed a technology for increasing the conducting ratio of the transistor 407 to a predetermined value .alpha.% (about 10%) before the start of the gradual increase control as disclosed in, for example, Japanese Unexamined Patent Publication No. 2-32726.
FIG. 6 is a waveform view when the conducting ratio is increased to the predetermined value (.alpha.%) just before the gradual increase control.
In this case, the switching duty (conducting ratio) for intermittently controlling the field current IF is not gradually increased from 0% but it is abruptly increased to .alpha.% (about 10%) in order to that the field current IF (generated current) is increased at an inclination faster than that in a gradually increasing time and thereafter gradually increased at a certain inclination.
With this operation, although the drop of the battery voltage VB is suppressed to some degree, since the conducting ratio is set to the relatively low value of .alpha.% (about 10%) at the beginning of the control, the insufficient charge of the battery 9 cannot be sufficiently compensated.
Further, since a certain degree of delay is caused during a time until the generated current is increased by .alpha.% as compared with a controller in which the field current IF is not gradually increased, the drop of the battery voltage VB is also increased.
As described above, the conventional vehicle generator controller, which simply gradually increases the generated current when the electric load is turned on, has a problem that the battery voltage VB greatly decreases at the beginning of the control, which makes the driver uncomfortable.
Further, the conventional vehicle generator controller, which increases the generated current (corresponding to the field current IF) to .alpha.% (about 10%) at the inclination faster than that when it is gradually increased before the field current IF is gradually increased at the certain inclination when the electric load is turned on, has a problem that the battery voltage VB also greatly drops because the insufficient charge of the battery is not sufficiently compensated although the drop of the battery voltage VB is slightly suppressed.
An object of the present invention made to solve the above problems is to provide a vehicle generator controller which suppresses a response torque shock caused when an electric load is turned on as well as sufficiently suppresses the drop of a battery voltage.